Ironwolf 3TB/4TB compatible with Nv+ v2?

Netgear doesn't update the HCL for legacy ReadyNAS, so the list hasn't been updated for some years now.

Seagate Ironwolf drives should work well in your v2, as would Western Digital Reds.  Both models are intended for NAS use.  While they don't have the performance of enterprise-class drives, they also are quieter, use less power, and run at lower temperatures.  Their performance is well-matched to your NAS.

Many of the newer drives are using "alternative mount points" - so you might find that some of the mounting holes on the drive aren't aligned with the holes in your disk trays.  Some will align, and that should be enough to securely mount the disks.

I'm not sure what the size limit in your NAS is.  I've seen some folks here post that they've installed 6 TB drives successfully.  There are some expansion limits that apply to your NAS though - XRAID won't expand a volume over 16 TiB, and there is also a growth limit of 8 TiB from your volume's initial size. 

4x4TB gives you a 12 TB (10.9 TiB) volume - so you wouldn't reach the first limit, but you could hit the second one.  If you do, then expansion will fail - and you'd need to do a factory reset to use all the space on the new drives.  That's destructive, so you'd need to make a full backup of your files first.